There's alwaysCan't offer much help as we barely got him down, but hopefully that helps.3 guardians with the buff, so divide your fireteam accordingly when you receive them, left-middle-right, one guardian at each position needs to have the buff. Get the first stun in and he won't appear on that spot again so let's say he appears right, then the buffs are shuffled while shooting at him there needs to be buff at left and middle, there is always 3 buffs so that makes it easier, but the shuffle can be really confusing and your fireteam will need good communication. Person in middle with the buff has hardest job as there's the front and back middle he can appear on.
Yeah, that was what we were doing. At least we're not missing anything.